Microwave Diagnostics of Fluctuating Low-Temperature Plasma with the Help of an Open Slowing Structure

A modified method of microwave diagnostics of low-temperature plasma is described. The method utilizes the filtering properties that an open slowing structure shows in the presence of plasma. The edge of the filtering band depends on the medium's permittivity. This simplifies the determination of the plasma electron density, because the spatial resolution is substantially higher than in conventional diagnostic techniques based on the free propagation of a microwave beam. A prototype of the plasma density sensor operating in the 3-cm wave band has a sensitivity to the electron density of ∼108cm–3; the resolved volume is ∼1 cm in diameter and 4 cm in length. A procedure is developed that enables the recording of the fluctuations of the plasma density near the sensor.